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What network adapter do you have in the laptop? Or at the very least, what model laptop do you have? I would guess your laptop is on some short of b/g/n mode which isn't compatible with the routers g/n mode.
Did you change the WiFi mode on the 655 router too? You should start with the 655 router first and make the changes there.
I would make sure the drivers are up to date for that device and wireless card on the PC. Does the wireless card on the PC support 5Ghz? Just because you see it there doesn't mean it's supported. I would contact the OEM Mfr of that PC and check.Also for 5Ghz, the 655 doesn't have a 5Ghz radio, only 2.4Ghz.
Nope can be either, just depends on what router you got and the features it supports.